Embodiments of the present invention relate to communication systems of the type having multiple transmitting and receiving devices that share a common communication medium; and, to methods for establishing communication in the presence of large numbers of such devices.
Conventional data communication systems have been applied to accomplish object identification using the medium of radio broadcast. Such radio frequency identification (RFID) systems find application in the fields of materials handling, inventory control, and generally in the field of tracking personnel, objects, and animals. In an exemplary arrangement, such a system may include an interrogator and several thousand transceivers, each transceiver being packaged as a disposable label or tag and placed on an object, animal, or person to be tracked. Each transceiver is manufactured using integrated circuit technology, programmed with a unique identifier, and assembled with a printed circuit antenna to form a flat assembly for incorporation into the label or tag. Typically, the interrogator has a fixed location, while transceivers are moved from time to time in and out of the communication field of the interrogator. It is highly desirable to accurately and quickly identify transceivers from a population of transceivers which may number in the billions. At the same time, it is highly desirable to reduce the cost of each transceiver to an absolute minimum.
Accurate and reliable detection of transceivers is made difficult by a number of factors including, for example, (a) transceivers have a limited amount of power available to operate when required to respond with a radio transmission; (b) the orientation of the transceiver antenna may be unsuitable for absorbing sufficient power from the signal transmitted by the interrogator; (c) the orientation of the antenna of the transceiver may be unsuitable for providing a transmitted signal sufficient for accurate reception by the interrogator; (d) cooperation of a transceiver with the interrogator may require sophisticated logic in the transceiver to accurately perform the transceiver""s portion of a communication protocol used to obtain an open communication channel between the interrogator and a single transceiver; and (e) transceivers transmitting simultaneously may cause a so-called collision.
There remains a need for a communication system suited for coordinating the use of a common medium among potentially billions of transceivers for interrogation or control activities to be accomplished in a limited time. In addition, there remains a need in some applications to minimize the circuitry, firmware, and software complexity required at each transceiver, to extend the operating range of communication, and to support larger numbers of individual identification numbers perhaps at the expense of complexity at the interrogator. Without these improvements, the size and cost per transceiver cannot be reduced to permit new and improved communication systems that employ inexpensive disposable transceivers such as identification tags, baggage tags, inventory labels, and the like.
A system in one implementation according to various aspects of the present invention includes a monitor and a plurality of transceivers that communicate over a common medium. The monitor includes a first transmitter, a first receiver, and a processor. Each transceiver includes a resonant circuit, a transmitter, a receiver, and an antenna coupled to the resonant circuit. The processor performs a method for performing transceiver communication that includes the steps of: (a) transmitting from the first transmitter a first frequency for a first duration; (b) after lapse of the first duration, receiving via the first receiver a response signal from at least one of the resonant circuits; (c) determining a second frequency from the received response signal; and (d) performing transceiver communication using the second frequency.
Transceivers of the type having a resonant circuit coupled to an antenna, when operating in close proximity to each other, may interfere with the response from a single transceiver by absorbing the energy intended to be received by the transceiver, absorbing the energy transmitted by the transceiver, or altering the resonant frequency of the resonant circuit. By determining the second frequency for transceiver communication, the monitor may establish communication with the single transceiver at a frequency better suited for transferring operative power to the transceiver, for conducting an interrogation protocol for identifying the transceiver, or for data transfer. Communication is maintained in spite of variation in the resonant frequency of the resonant circuit which may arise from coupling as discussed above or from variation in manufacturing and operating environment (e.g., temperature, humidity, relative movement, or component aging).
The monitor may further include a first antenna coupled to the first transmitter and a squelch circuit for dissipating energy on the antenna after lapse of the first duration and before receiving from the first receiver the response signal from the resonant circuit. By quickly dissipating energy, the response signal may be more quickly and accurately received by the second receiver and consequently the second frequency may be more quickly and accurately determined, increasing system sensitivity and reliability. Obtaining quicker receiving from the second receiver extends the operating range of the monitor or permits operation with weaker signals. Weaker signals may originate from transceivers located further from the monitor or in an orientation that is detrimental to reception by the first receiver. Such detrimental orientation of the antenna in the transceiver may be with respect to the first antenna of the monitor or with respect to other transceivers proximate to the transceiver antenna.
The monitor may further include the second receiver providing phase detection, or a signal analyzer provides phase detection. Phase detection providing phase information regarding the received response signal. The processor may further determine the second frequency in accordance with the phase information. Phase information varies over a wider range of values near a resonant frequency. By determining the second frequency in accordance with phase information, the second frequency may be more accurately determined. Communication with a more accurate second frequency improves the efficiency of transferring operative power to a transceiver, permits faster or more accurate identification of transceivers, extends the operating range of the monitor, overcomes problems of detrimental orientation discussed above, or permits faster or more accurate data transfer between the monitor and a single transceiver.
When each transceiver has a respective identification number comprising a common total number of portions, a method of determining an identification number of a transceiver of a plurality of such transceivers in one embodiment according to various aspects of the present invention includes the steps of: (a) transmitting a start signal; (b) receiving a reply at a time after the start signal; (c) determining a number in accordance with the time determined in step (b); (d) transmitting a start signal and the number determined in step (c); (d) repeating steps (b) through (d) until a count of performances of the step of transmitting is not less than the common total; and (f) determining the identification number in accordance with each reply.
By repeating the steps of transmitting a number of times not less than the common total, a step of detecting whether a collision occurred is not necessary. The reply may convey no more information than the fact that a reply has been made, thereby eliminating the need for a longer duration of reply. By dividing an identification number into portions and applying the protocol discussed above, a large number of unique identification numbers is practical (e.g., 240 in 4 10-bit portions) without increased complexity or cost in each transceiver.
A short reply duration is associated with several advantages. More replies may be received in a given time period, increasing the likelihood of identifying transceivers that are only briefly in range of the monitor; redundant replies may be used to increase system reliability; and the amount of power needed in each transceiver to transmit a reply may be reduced.
Lower power consumption is associated with several advantages, including: transceivers with lighter weight, smaller size may be practical at lower cost; and the communication range may be extended by expanding the power budget used for receiving or transmitting or both.
Extending the communication range has additional advantages, including: increasing the time permitted for communication for transceivers that are only briefly in range; decreasing the adverse affects of detrimental orientation as discussed above; permitting closer proximity between transceivers; permitting larger numbers of transceivers in close proximity to each other; reducing the size of antennas; and decreasing the number of monitors or antennas that may otherwise be needed to provide communication in a large area.
The method of determining an identification number may include a step following step (b) for rejecting an invalid reply. Further, time domain or frequency domain techniques which may be employed in the process of determining a second frequency in the method for performing transceiver communication may be used in the process of determining an identification number in the step of rejecting an invalid reply.
A transceiver in one implementation according to various aspects of the present invention includes a resonant circuit (having a resonant frequency), a receiver, a memory, a comparator, a counter, and a transmitter. The resonant circuit includes an antenna used for receiving and transmitting. The receiver, coupled to the resonant circuit detects a start signal followed by indicia of a first code. The comparator provides a result of comparison responsive to the first code and a second code provided by the memory. The counter is loaded with a count provided by the memory and provides a completion signal after a duration in accordance with the count. The transmitter transmits a reply in response to the result of comparison and the completion signal.
When the second code maps to a transceiver identification number, such a transceiver identification number may be determined without the transceiver transmitting the second code. The duration of transmitting the reply is, therefore, brief with advantages as discussed above.
When such a transceiver is used with the system described above and the resonant circuit is used to establish the frequency for transmitting, the first receiver of the monitor may selectively receive in a reduced frequency band expected to include the reply. Improved receiver sensitivity with concomitant improved range of reception results.
A transceiver may further include a phase locked loop that locks to the frequency being received, maintains the locked frequency in the absence of received signal, and drives the transmitter to transmit at the maintained frequency instead of the resonant frequency. Improved range of transmitting by the transceiver may be obtained. Improved communication may be obtained as a consequence of being able to provide operative power, determine identification, and provide data transfer at a frequency different from the resonant frequency particularly when the resonant frequency is being affected by detrimental orientation as discussed above.
By transmitting a reply in response to the completion signal, a numeric value may be communicated from the transceiver to the monitor with a numeric resolution in accordance with the duration from the start signal. For example, multi-bit digital values may be communicated with a 1-bit reply.
A monitor in one implementation according to various aspects of the present invention includes a processor for communication with a plurality of transceivers, an event detector, a plurality of receivers, a plurality of transmitters, and an antenna network controller for coupling the monitor to a provided antenna network. The processor may include a first and a second processor coupled for data transfer by a computer network. The processor may determine the location of a transceiver in a zone monitored by an event detector in response to a signal provided by the event detector in cooperation with transceiver communication as discussed above. Multiple receivers provide simultaneous narrow band detection for receiving a signal in accordance with a predetermined phase. Multiple transmitters provide each of multiple simultaneous or sequential transmissions, each on a respective antenna (or group of antennas) and at a respective amplitude, frequency, and phase which may vary from other respective transmissions.
An antenna network in one implementation according to various aspects of the present invention includes a plurality of antenna nodes coupled to an antenna bus. Each antenna node includes a plurality of transceiver channels and a coupler for coupling each transceiver channel to a provided plurality of antennas. Each transceiver channel includes a squelch circuit. When the squelch circuit is located proximate to a point in each of several antennas, out of band energy related to squelching is reduced. In another implementation, the squelch circuit includes a plurality of current sources for each of leg of an antenna to be squelched.
An antenna network node in another implementation according to various aspects of the present invention includes a cross-channel coupler and a transceiver channel that includes a difference amplifier for signal processing proximate to provided antennas.
An antenna network in another implementation according to various aspects of the present invention includes an antenna bus, and a plurality of network nodes each comprising a processor, a tuner, and a coupler for coupling provided antennas to the tuner. The bus conveys a signal having indicia of a command with settings. The processor directs operation of the tuner in accordance with the settings. In another implementation, a conductor of the bus conveys at a first time indicia of the command and at a second time indicia of a signal to be transmitted.
A passage in one implementation according to various aspects of the present invention includes planar antennas each arranged at a respective angle to provide in combination a minimum received signal greater than a predetermined amount for all possible orientations of a transceiver in the passage. In an alternate implementation, each antenna includes a Q modifying circuit that facilitates wider-band reception than transmission.
A carrier in one implementation according to various aspects of the present invention includes an antenna and a series capacitor for tuning the antenna. Enhanced transceiver communication results when transceivers are placed in the carrier. In an alternate implementation, a carrier includes a first and a second antenna each with a respective tuning capacitor. The first and the second antenna are coupled to cooperate. Energy received in a first pattern is re-radiated in second pattern for further enhanced transceiver communication.